1. Field of the Invention
The invention relates to a system and a method for transferring electric energy to a vehicle, in particular to a track bound vehicle such as a light rail vehicle (e.g. a tram).
The system comprises an electric conductor arrangement for producing an alternating electromagnetic field and for thereby transferring the energy to the vehicle. The conductor arrangement comprises a plurality of consecutive segments, wherein the segments extend along the path of travel of the vehicle.
2. Description of Prior Art
In particular track bound vehicles, such as conventional rail vehicles, mono-rail vehicles, trolley busses and vehicles which are guided on a track by other means, such as other mechanical means, magnetic means, electronic means and/or optical means, require electric energy for propulsion on the track and for operating auxiliary systems, which do not produce traction of the vehicle. Such auxiliary systems are, for example, lighting systems, heating and/or air condition system, the air ventilation and passenger information systems. However, more particularly speaking, the present invention is related to transferring electric energy to a vehicle which is not necessarily (but preferably) a track bound vehicle. Generally speaking, the vehicle may be, for example, a vehicle having an electrically operated propulsion motor. The vehicle may also be a vehicle having a hybrid propulsion system, e.g. a system which can be operated by electric energy or by other energy, such as electrochemically stored energy or fuel (e.g. natural gas, gasoline or petrol).
Track bound vehicles, in particular vehicles for public passenger transport, usually comprise a current collector (alternatively a device) for mechanically and electrically contacting a line conductor along the track, such as an electric rail or an overhead line. At least one propulsion motor on board the vehicle is fed with the electrical power from the external track or line and produces mechanical propulsion force.
Trams and other local or regional trains are operated usually via overhead lines within cities. However, especially in historic parts of cities, overhead lines are undesirable. On the other hand, conductor rails in the ground or near the ground cause safety problems.
U.S. Pat. No. 5,821,728 describes an apparatus for charging batteries of a moving electric vehicle comprising a series of inductive coils for producing a magnetic field along a centerline of a roadway. The inductive coils are connected to power lines via switches that can be activated by switch activator sensors. When a sensor receives a signal from a transmitter of the vehicle, this will cause the corresponding switch to close and thereby to activate the coil.
However, since the coil produces an electromagnetic field the power supply lines are connected to an alternating voltage source. Consequently, the power supply lines permanently produce an electromagnetic field of smaller intensity than the coils, but still strong enough to interfere with any electric or electronic equipment in the surrounding.
Inductively transferring energy from the track to the vehicle, i.e. producing electromagnetic fields, is subject to restrictions regarding EMC (electromagnetic compatibility). On one hand, electromagnetic fields may interfere with other technical devices. On the other hand, people and animals should not be subjected to electromagnetic fields permanently. At least, the respective limit values for field intensity must be observed.
Alternatively, the power supply may be a DC (direct current) power supply line which may be connected to each coil via an inverter. Typically, inverters comprise a control device for controlling the operation of semiconductor switches in order to produce the alternating voltage on the AC (alternating current) side of the inverter. This control device also requires electric energy for operation.
In order to reduce the electromagnetic emission where no vehicle is driving at a time, the conductor arrangement (e.g. the arrangement comprising the coils according to U.S. Pat. No. 5,821,728) which is used to inductively transfer the energy to the vehicle can be divided into consecutive segments extending along the path of travel of the vehicle. These segments may be operated where required only. In particular, the length of each of the segments along the path of travel may be shorter than the length of a vehicle in the travel direction and the segments may be operated only if a vehicle is already occupying the respective region of the path of travel along which the segment extends. In particular, occupied by a rail vehicle means that a rail vehicle is driving on the rails along which the segment extends. Preferably, the segments are operated only if the vehicle is fully occupying the respective region of the path of travel. For example, the rail vehicle is longer (in the direction of travel) than the segment and the vehicle's front and end are driving beyond the limits of the segment, if viewed from the center of the segment. Therefore it is proposed that the segment is switched on (i.e. the alternating current through the segment is starting to flow) before a receiving device of a vehicle for receiving the transferred energy enters the region of the path of travel along which the segment extends.
If a large number of consecutive segments is provided, using a DC power supply line means that an equally large number of inverters is required. Each inverter needs to be provided with electric energy for operation. Therefore, additional equipment for conducting electric energy to the inverter's control device is required.
It is an object of the present invention to provide a system of the kind indicated above, for inductively transferring electric energy to a vehicle and to provide a method of transferring electric energy to a vehicle, which reduce the effort for providing electric energy to devices of the system which control and/or operate the generation of electromagnetic fields in order to transfer the energy to the vehicle. Furthermore, the respective limits for meeting EMC requirements shall be met.